Johnson 115 Temperatures - Help

[Needmorerum]

Looking for some advice (as usual), the Johno 115 I have on my Cruise Craft seems to overheat at times. It doesn't do it at idle, only when up at speed. It is a 98 OMC Johnson 115 Oil Injection.
It was usually only if I had it up around 5500rpm, but over the weekend it heated up at cruising speed, around 4000rpm. The boat was loaded with 4 adults and 3 kids, and a couple of eskies for a day over at the island.
I spoke to the bloke I bought it off, and he reckons that he did have some problems with it, great of him to tell me now, but it was only shit getting stuck around the temp sender or something similar.
I have been gauranteed that the overheating alarm works, and that if it is shut down as soon as this alarm comes on then it will do no damage. I believe this, but I do believe that this would shorten the life of the motor.
When the temp rises, I found that by backing off and going back down to idle, that the temp starts to come back down to normal operating temp straight away.
I had this checked out last service, and the mechanic that serviced it, said that there has obviously been a problem at some stage, as the thermostat has had a hole drilled in it. The water pump was checked at the same time and there was nothing wrong with it either. Not sure what this could be.
I have done a couple of trips since the service and it seemed to be OK. It played up again yesterday, so the problem is still there.
Hopefully someone can lead me in the right direction, it goes in again tomorrow to be looked at again.

Any help would be appreciated,
Corry

PS appologies for the long winded story

[peterbo3]

Corry,
Overheating can be caused by a heap of things but most common is worn impeller. How long since replacement? Do you have a temp guage & a water pressure gauge? There are so many possibilities-all beyond me.
Go here http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi. These people have covered every known problem.

[Needmorerum]

Not sure how old it is, but the mechanic reckons the impellor is OK. I am going to get him to change it tomorrow just for a datum.
I have the temp gauge, but not a water pressure gauge. I do know that I can't run it for more than a couple of minutes on the earmuffs. Temp starts to raise straight away, and I shut it off when it reaches just over half way.

Hopefully they can come up with something during the week.

Corry

[Outsider]

Corry,

Had exactly the same motor on my Outsider and it had exactly the same problem when I bought it. Ran pretty hot all the time and got hot real quick on the muffs. I had the impeller replaced but the mechanic said that he needed to drill a hole in the thermostat to allow it to open earlier (apparently the factory item thermostats aren't available so everyone uses a generic one that's not quite right) and that fixed it for a while.

About 3 months later it got reeeeeeeeel hot coming back from Moreton and was eventually diagnosed as a faulty impeller - the plastic/rubber vanes had come away from the metal sleeve in the centre.

I was glad to see the back of that motor - thirsty, dirty and hot just about sum it up.

Good luck - I hope yours is better behaved than mine!

[Hagar]

Corry
Here is something for you to consider if everything with the impeller and thermo's checks out .

My local Yamaha dealer has had a couple of engines with overheating problems that only showed up at wide open throttle or thereabouts . Below that they ran fine . After running out of possibilities after checking or replacing impeller , thermo's etc. it was put down to salt residue buildup in the water jacket around the cylinder bore . Sure enough when the head was pulled off ( on these you can isolate which side is triggering the buzzer by dicconnecting one temp sender at a time ) the buildup had partially blocked the jacket enough to overtemp at high engine load ) . Blockage cleared and problem fixed - finally .

Even with diligent flushing this happened . Cold tap water will keep the thermo's all but closed when flushing and very little fresh water is circulated thru the block water jacket and thus the problem on these motors . Johnno may be different - I don't know .

This job costs afew bucks so get your mechanic's opinon first when you have exhausted all the simple cheaper possibilities .

Chris

[peterbo3]

Webby had a similar problem on his V4 Yammie. Turned out to be crud in the cooling galleries in the head. I believe there was little change from a $K

[Paul_C]

Had a similar problem years ago with a 65 Merc, the guy I bought it from provided me with an invoice for a shitload of work he'd had done to it, including new impellor, by a marine dealership, it nearly seized up on me one day and after allowing it to cool down I limped home. In a nut-shell what I found when I pulled the leg apart was the impellor was in back to front and the seals around the tube from the pump to the powerhead were missing. So much for Marine Mechanics, because this Motor Mechanic, found the problem they left behind.

Paul Cade

[Needmorerum]

Well here's an update. The thermostat already has the hole drilled in it. And the pump impellor is fine. I spoke to the mechanic today and he is at a loss, without going in for a look. With having a tad over 500 hours on it, it has been suggested that it may be worth a look and a change of o-rings anyway. This was from someone else, and the mechanic agrees. I was going to do this soon, so I have given them the OK to strip it further to have a look and change the o-rings. With a bit of luck this will fix the problem.
I have asked if there is any problems with me coming in to take photo's while it is apart, and they have no drama's, so I hope I can get away from work and get over there when they have it apart. Failing that, I will get them of an afternoon after work.
Dollar wise, they have told me to expect around the 250-300 mark. Hopefully back for the weekend, as the weather is starting to look alright. Typical, when you decide to put it in for a look, the weather fines up.

Will keep you posted,
Thanks for the replies
Corry

[aido]

it would be interesting to get his thoughts on your trailer springs as well.

[Needmorerum]

I asked him about it, all the trailers they have in there are Dunbiers' which have the twin slipper set up. And he said that he doesn't really take much notice of springs on trailers when boats come in for servicing or work.
Can't blame him, I never looked at anyone else's springs until now either.

Corry

[NQCairns]

Corry, have you tried touching the engine when the alarm sounds to see if it is really in overheat and where the overheat is? sometimes it can be a hot spot due to an air bubble and specific to near the sender, but hard to assume by touch. I have no idea what your particular problem is.
The drilling of the air bleed hole is redundent after the first 10 minutes of operation and has no bearing on cruise etc overheats.
Centre your investigation on the poppet valves if nothing else turns up, they handle high speed stuff.
I am sure that most companys keep quality feedback away from our dashboards to promote parts sales .
You need a water pressure guage and a numbered and calibrated temp guage each set to an adjustable alarm switch. If there is a waterpressure guage on board the temp guage can almost be ignored. How do you know it is even overheating? really!
Have you used any of the flushing additives in the past?? Have they backflushed it? Done any dredging of sand/silt lately, what about the previous owner - some people do stupid things
You need to get them to pull the heads, no choice now if all is checking out as you say, be thankfull it is not a 4 $troke.
good luck, interested to know what the wsh up is, if you find it. nq

[mako_5.2]

Try checking your thermostat. Suspend it in a pot of water on the stove and warm it up check it against a thermometer and see if it opens at the right temp. It should at least open before it boils if you dont have a thermometer. Even worth checking new ones before you put it in.
Good luck

[mini696]

The hole in the thermostat is there to allow fluid to flow before the thermostat opens. It doesn't actually make the thermostat open any earlier than usual.

If a thermostat is overheated the spring in it can be affected, this causes it to open at a later temp than normal.

I had this problem on my car once. It over heated (to 3/4 on the dial) because of a cracked tank. From that day on the the temp guage would get to half way before the thermostat would open (usually was 1/4). Over time this caused the thermostat to keep getting worse and worse until eventually it wouldn't open until the guage got to the top.

I am sure your mechanic may have checked this, but I would double check it to be sure.

If you want to check the thermostat, put it into a saucepan of water -with a thermometer- and heat it up until the thermostat opens. This is the temp it will open on your boat.

I dont know what a good running temp is on your boat, maybe someone on this site can help you.

[Needmorerum]

Well it's in now and has the heads off. The water jackets look good, the thermostat tested fine.
Waiting on the seals and gasket kit to arrive tomorrow. Hopefully all will go back together OK. Being flushed and back flushed before they have finished with it. Didn't want to backflush anything before hand as I wanted to have a look to see what the jackets were like.
If there is still a problem after this, I'll be on the hunt for a water pressure gauge and start testing the sender units.
As far as trying to touch it nq, no I haven't, I have only let it go high enough for the alarm to sound once. That was on the muffs at home. I shut it down and and didn't fire it up again after that. In the water, it gets up to the very top of the gauge, and doesn't go any higher to set off the alarm.
I'm now starting to doubt the gauge. Time will tell, will have it back after the weekend, so will take it for a run next week.
It was due for o-rings and a check, it has hit the 500 hour mark, so all isn't wasted.
Will keep you posted.

Corry

[NQCairns]

Corry just a thought while the engine's apart - are the water deflecters fitted, sometimes things get forgotten in manufacture, longshot but worth noting anyway.
I would be replacing the sender unit as well at this stage, gotta do what you can do while you can or go with one that bolts to the outside of the engine and touches the block.
It really is worth it to spend the time and get used to how hot running temp feels on your engine byt touch or use a handheld lazer pyrometer, those engines can overheat only one side at a time also.
Bloody costly exercise this type of investigation, sounds like you will have a great engine when it's nutted out.
High 70s C is overheat I think and low 70s to middle is running temp with 80 deg C + well into overheat, these numbers are just from memory so dont take them for gospel, different model outboards do run differing operating and overheat temps not like cars where just above boiling point is the limit. nq